The invention is directed to a measuring system comprising a measurement transducer and a following control device wherein a measured value is allocated to a parameter being measured (the "measured parameter"). The measurement transducer has an individual characteristic associated with it and contains a sensor for the measured parameter. The measurement transducer supplies an electrical measured signal dependent on the measured parameter.
A known measuring system of this type is disclosed in EP 079,086, incorporated herein. The measurement transducer represents a unit formed of the sensor and of a coding memory that contains characteristic data for the sensor. These characteristic data are, for example, the values for the null drift, the temperature behavior, etc., of the sensor signal referred to as the values of a standard sensor signal. The control device connected to the measurement transducer interrogates the content of the coding memory and corrects the sensor signals coming from the sensor therewith. This occurs by linear changes of this sensor signal in the control device over the entire bandwidth of the possible sensor signal (influence on gain factors or offset of operational amplifiers and adding up signals).
Such a measuring system is well-suited for the utilization of sensors having linear characteristics. Given employment of sensors having a non-linear characteristic, however, it is no longer possible to correct the sensor signal with identical correction values over its entire bandwidth.
The invention is, therefore, based on the object of providing measuring equipment such that sensors having a nonlinear characteristic can also be employed.
The invention proceeds on the basis of the consideration that a type characteristic can be identified for every type of measurement transducer which fundamentally identifies all measurement transducers of the same type. In accordance with the invention, this type characteristic is defined by type data that are stored in a type memory of the control device. The deviations of the individual characteristic of a measurement transducer from the type characteristic are identified by discrete individual values and accompany the measurement transducer in a coding memory. A computer in the control device then determines a reference point on the individual characteristic from every individual value and from the type characteristic. Proceeding on the basis of these reference points, a measuring program in the program memory of the computer subsequently determines the allocated measured value for every measuring signal.
For this purpose, the measuring program can be fashioned such that an identification regarding the two reference points of the individual characteristic between which a measured value lies is first identified given an incoming measured value. Subsequently, the measured value is identified by one of the known interpolation methods, for example by linear interpolation between the two reference points.
When the measured values must be supplied at a very short interval following one another, then the method set forth presumes a very fast computer. Under such circumstances, it can then be more expedient to first calculate all possible point value pairs of the individual characteristic with a calibration program proceeding on the basis of the individual values and of the type characteristic, and to deposit these in the main memory of the computer such that the corresponding measured parameter for every measured value can be directly read out therefrom.
The invention has particular significance given measurement transducers having a non-linear characteristic. However, it can also be advantageously employed in measurement transducers having a linear characteristic. In this case, for example, one manages with two individual values of which one indicates the axial shift of the individual characteristic compared to the type characteristic in the direction of the abscissa or ordinate, and the second individual value indicates the slope of the individual characteristic.
Any means which contains one or more individual values coded such that at least one individual value can be interrogated and decoded by the evaluator comes into consideration as a coding memory. A simple example is a connecting terminal strip whose posts are partly insulated and partly grounded, so that the connected evaluator can identify a binary number by a resistance measurement via the individual posts. Electrical components such as, for example, capacitors, resistors, etc., come into consideration as analog memories for the coding memory that can be electrically interrogated by the evaluator.
In one embodiment of the invention, the type characteristic is stored as a mathematical characteristic function in the type memory that defines the type characteristic of the measurement transducer with m parameters. The evaluator supplies the m parameters (constants) of this characteristic function by the m individual values from the coding memory of the measurement transducer, these being selected such that the characteristic function of the individual characteristic of the measurement transducer arises therewith.
In an embodiment of the invention described hereafter, the type memory contains the type characteristic in the form of discrete point value pairs and the coding memory contains the deviations of the individual characteristic from the type characteristic for given reference points.